POSTPRANDIAL APPEARANCE OF DIETARY DEUTERATED CHOLESTEROL IN THE CHYLOMICRON FRACTION AND WHOLE PLASMA IN HEALTHY-SUBJECTS

This study examined the appearance of dietary cholesterol in the chylo micron fraction (chylomicrons plus chylomicron remnants) and whole pla sma in healthy normolipidemic subjects during a 0-7-h postprandial per iod. Six adult males were given two diet sequences in random order: a low-fiber diet (standard Western diet for 14 d) followed by a labeled low-fiber test meal or a fiber-supplemented diet (40 g oat bran/d for 14 d) followed by a labeled oat bran (40 g) test meal. The test meals provided 192.5 mg cholesterol, including 80.1 mg octadeuterated choles terol. Fasting and hourly postmeal blood samples were obtained for 7 h . Isotopic cholesterol ratios [tracer:(tracer + native cholesterol)] w ere determined by gas chromatography-mass spectrometry. Chylomicron tr iacylglycerol and cholesterol concentrations peaked after 2-3 h and re turned to baseline after 7 h. After the low-fiber test meal, the isoto pic cholesterol ratio continuously increased until 7 h in the chylomic ron fraction (4.2 +/- 1.2 x 10(-3)) and whole plasma (1.04 +/- 0.39 x 10(-3)). At 7 h postprandial, the maximum dietary cholesterol concentr ation in the chylomicron fraction and plasma cholesterol was 1 in 99 a nd 1 in 397 cholesterol molecules, respectively. No marked differences were obtained after the high-fiber sequence compared with the low-fib er one; there was a comparable isotopic cholesterol ratio and concentr ation in the chylomicron fraction and a slightly lower (-44%, P < 0.10 ) 0-7 h area under the curve whole-plasma deuterated cholesterol conce ntration. Thus, dietary cholesterol supplied as a single meal does not simultaneously appear in the chylomicron fraction postprandially with endogenous cholesterol and triacylglycerols and fiber feeding does no t markedly alter this process in healthy normolipidemic humans.